1. Field of the Invention
The present invention generally pertains to telecommunications networks and in particular to interconnection between an MS-SPRING network and a High-Order SNCP ring network.
2. Description of the Prior Art
In modem telecommunications networks it is becoming extremely important to have the possibility to repair the failures occuring in the networks themselves without impairing the functionality of the service. Therefore ring architectures are more and more frequently used and furthermore the telecommunications networks are generally provided with protection means against possible failures of their components.
In the SDH MS-SP (Multiplex Section Shared Protection) RING networks, for instance, a distributed protection mechanism is implemented that allows the automatic traffic restoration should a fault occur in the connection fibers. In other words, the MS-SP ring networks perform the automatic traffic restoration through a synchronized re-routing of said traffic, which is carried out at each node of the ring. This operation is controlled by a protocol consisting of messages that are continuously exchanged between adjacent nodes. Said protocol and the related operations are defined by several international standards, issued by ANSI, by ITU-T and by ETSI, and they are characterized by a certain set of rules and messages. See for instance the ITU-T Recommendation G.841.
An SNCP ring network (see definition 3.31 set forth in ITU-T Recommendation G.805) is a ring network with a type of protection which is shaped by a sublayer generated by expanding the connection point of the subnetwork (where, by “subnetwork” is meant that topological component used to carry out the routing of a specific characteristic information).
One of the most important network architectures is composed by the interconnection of ring networks using a “Dual Node and Drop & Continue” architecture, namely, an architecture where two nodes of each ring are interconnected. The “Drop & Continue” function that is a function that is implemented within a node wherein the traffic is dropped from the working channels on the ring and, at the same time, continued over the ring.
The classic solution provides for four network elements or nodes (two for one ring and two for the other ring) that are interconnected through STM-N interfaces; however, through the use of large ADMs (Add Drop Multiplexers) or DXCs, (Digital Cross Connects) that substantially integrate two nodes and operate as ring closures, it is possible to reduce the overall number of interconnection nodes to two. In this case the interconnection is done in the network element matrix without using the STM-N interfaces.
The “Dual Node and Drop & Continue” architecture is known from the ITU-T Recommendation G.842 but such a Recommentadion only provides for the case of four separate interconnection nodes. Even if one would integrate two nodes into one (thus avoiding the use of STM-N interfaces) this solution would have the same inconveniences from a management point of view since three selectors for each circuit should be anyway used and managed. Another drawback of this possible solution wherein two nodes are integrated into one is that it would be expensive in terms of fiber utilized and band exploitation.